Memory LCDs for e-books and reading devices

Sharp has introduced memory LCDs in new sizes and will soon unveil a 6.02in model suitable for the e-books market and other portable reading devices.

The recently introduced models comprise two 2.7in (6.9cm) displays (LS027B4DN01 and LS027B4DH01) with a resolution of 400 x 240 pixels and a 2.94in model (LS029B4DN01) with a resolution of 456 x 240 pixels.

For the e-books market, the company intends to supplement the range with transflective and touch-screen models in the second half of the year.

Unlike the usual reflective-memory LCDs, transflective-memory LCDs offer the option of adding backlighting so that e-books or other applications can also be used in the dark.

Thanks to the capacitive touch screen, e-books can be designed in such a way that readers can turn the pages almost like a paper book.

In addition, a 4.4in model is in preparation for the autumn.

These system LCDs are based on Sharp's own Continuous Grain Silicon (CGS) technology.

This enables it to equip each pixel with a 1-bit memory that stores the image information uploaded onto the screen.

Image information therefore only needs to be rewritten in those pixels in which the content has changed compared to the previous picture frame.

As reflective displays, Memory LCDs do not require any backlighting.

The combined effect means that memory LCDs only have 0.8 per cent of the power consumption of conventional displays of the same size.

In contrast, with conventional LC displays, microcontrollers have to rewrite the entire screen content from frame to frame at a speed of 50Hz to 60Hz, even if most of the image content remains the same.

In addition, the backlight accounts for a good proportion of the power consumption.

Standard LCDs have a power consumption that is around 130 times greater than that of the newly developed memory LCDs.

A 1.35in memory LCD uses 15uW in operation, whereas a standard LCD of comparable size requires around 2mW to display an image.

The 6.02in model only requires up to 3.5mW at a frame frequency of 1Hz.

Unlike other reflective displays, this new type of LCD does not require any polarisers.

Thanks to a special polymer network liquid crystal (PNLC) material, the image is generated by the status of the pixel changing from transparent to white with a reflectivity of 50 per cent.

This gives the display a silver-metallic appearance that is said to be suitable for fashionable applications.

With a slightly more conventional version of the memory LCDs, polarisers and high-reflective (HR) liquid crystals are used.

They supply a purely black-and-white image with good legibility and a broad viewing angle.

Through their minimal consumption of power, small solar cells can supply sufficient electricity to run the new memory LCDs.

The new type of display is said to be an ideal solution for small portable applications, such as e-books, wristwatches, heart-rate monitors and other fitness devices and shelf labelling, for example.

With solar cells as a source of power, such systems can even be designed as self-sufficient applications.

In order to simplify the design-in for such energy self-sufficient solutions, Sharp also offers memory LCDs as 3V models so that, when operated with conventional lithium-ion rechargeable batteries, no charge pump is required in between.

The new 6.02in display is already designed for this supply voltage and four other memory LCDs that are expected to be launched on the market in the second half of 2010 also only require the lower supply voltage.

The new memory LCDs are already available in 1.35in, 2.7in and 2.94in diagonals from the sales offices of Sharp in Europe and through distributors.

Samples of the 6.0in models are anticipated to be available in the second quarter of 2010.

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